$\begingroup$Any reason why you are unsure? I don't think anyone will have any hard evidence, but isn't this one of those things so intuitive you don't need the community for it? I don't understand what kind of answer you expect. 'Why Not?' ? 'Some things need to evolve as well?' ? Please elaborate how this is an issue in your wb process and not just philosophizing$\endgroup$
– Raditz_35Dec 7 '18 at 17:38

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$\begingroup$You may be thinking too much about human speech. Just because we use consonants and so on does not mean anyone else has to communicate like that. Our speech evolved to exploit our physical and mental capabilities. You can be very expressive with sign language and with language forms that don't involve speech related nuances. You don't need to make their anus match human speech.$\endgroup$
– StephenGDec 7 '18 at 18:04

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$\begingroup$@chaslyfromUK Sorry, but this isn't addressing the concerns I had. Sorry for not being clear. I agree that this isn't a trivial question, I wonder how this can be answered in a reasonable way. It might be me thinking that those kind of questions are not what WB is all about - I don't get how this is an issue while building a world, I don't get why you don't just say: It sounds reasonable enough. Biology is too complicated for definite answers. If the actual problem you are facing (and not the reason why it's not used for speech currently) was clear, maybe someone could find a way around it$\endgroup$
– Raditz_35Dec 7 '18 at 18:52

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$\begingroup$@L.Dutch - Certainly related. However that's about humans using a simple code. I'm asking about an alien actually evolving this way to attain a complex language if the mouth route wasn't available.$\endgroup$
– chasly from UKDec 7 '18 at 19:28

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$\begingroup$I was not suggesting sign human language should be replace speech in your creatures. I was illustrating that non-verbal communication can be capable of a great deal of depth and complexity. Your creatures do not need to make human sounds or human gestures at all. They would evolve their own methods suitable to their own physical capabilities.$\endgroup$
– StephenGDec 7 '18 at 20:06

2 Answers
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It's a little boy's dream: talking through farting. But it may be a part of everyday life for herring. A new study finds that the fish make noise by squeezing air bubbles out of their backsides. Researchers believe the noise could be used for communication.

(...)

The team noticed that herring often release bubbles from their anuses when scared or during ascent or descent. They reported this curious finding earlier this year in Aquatic Living Resources.

To get an even closer look, Ben Wilson of Simon Frasier University in British Columbia, Canada, set up tanks in the lab. Wilson's group videotaped the fish and correlated the bubble blowing with the sounds they recorded, which they termed fast repetitive ticks (FRTs). Wilson's group found that the herring need to gulp air at the surface for continued FRTs; when the researchers blocked the herring's access to air, the fish FRTed for a little while then stopped. The team also noted that the herring made this particular noise just as darkness was falling, when they gather. This suggests that the FRTing has a social function, Wilson and colleagues report online 5 November in Biology Letters.

Your aliens could communicate by making pulses of different length and pitch. Pulse length can be controlled by regulating the amount of expelled gas; pulse pitch may be controlled by using more or less rectal length for the fart, or by controlling the anal aperture.

As for how to get the air in there, use a mechanism similar to aerophagia.

$\begingroup$Fascinating. This makes for a really good solution. Actually I was hoping to make my creatures aquatic but couldn't see how to do it. Swallowing air at the surface for a fish that presumably can stay submerged for ever is really unexpected. It makes you wonder how that could have evolved.$\endgroup$
– chasly from UKDec 7 '18 at 20:33

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$\begingroup$I really like Renan's contribution in general and I think that Renan is a much smarter person than I am, but still, how does this answer the question? I know the OP accepted it, but I don't understand the rules of this SE anymore :($\endgroup$
– Raditz_35Dec 8 '18 at 6:39

$\begingroup$@Raditz_35 question: "Could an alien anus-breather evolve to communicate entirely by taking in and expelling wind?" Answer: "yes, here is how an animal IRL does just that plus a refinement idea". I never post an answer that does not correlate directly to the question being asked.$\endgroup$
– RenanDec 8 '18 at 15:18

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$\begingroup$"I'm talking about a complex language similar to that of humans. Not just alarm calls." I still argue that this isn't a question that needs to be answered or can be answered, so I naturally disagree with that this is an answer. Also this doesn't add anything to the OP which also cites that some humans can basically do it$\endgroup$
– Raditz_35Dec 8 '18 at 16:42

While not impossible, the biggest problems with anus speaking is that the colon is designed to be filled with solid waste and you'd basically be unable to speak without purging first. A second issue is that if you are picturing a similar placement for the anus to that you find in most earth animals, you'd also have trouble speaking while moving since you have all those large gluteal muscles around it that flex and extend as you walk. If you think about human speech, it is not so much the faculty of our mouth to eat that makes it good for speech, but the fact that it ties into our respiratory system. Our respiratory system is always clear by design, and it is already very specialized at inhaling and exhaling large volumes of air for which there is not really an evolutionary pressure to cause that adaptation in the anus.

While it would certainly make for an entertaining plot point, and is not entirely unreasonable that this might happen, I can think of several other ways an organism would probably have a stronger evolutionary reason to develop communication than via the anus.

$\begingroup$I'm dubious this would be an entertaining joke for very long. E.g. it might be OK for a couple of gags in a Red Dwarf style episode, but will become tedious after that. YMMV of course.$\endgroup$
– StephenGDec 7 '18 at 18:32

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$\begingroup$Yeah, the purging part would make for a bad main character, but as a alien you encounter one or two times, it might be entertaining.$\endgroup$
– NosajimikiDec 7 '18 at 19:00

$\begingroup$I was inspired by reading about this turtle. Why Do Some Turtles 'Breathe' Out of Their Buttsseeker.com/… . Although the turtles breathe through their rear-end it doesn't seem to interfere with the other functions. That's why I thought an alien might do the same.$\endgroup$
– chasly from UKDec 7 '18 at 19:08

$\begingroup$Although I understand the references to humour, there is also a serious question here. Nature has come up with some pretty weird stuff on planet Earth. If an alien's mouth parts were simply completely wrongly designed for developing speech then I'm not sure what else might happen. With regard to an alternative such as sign language, that is very much a product of humans' manual dexterity. It wouldn't be available for, say, a quadruped.$\endgroup$
– chasly from UKDec 7 '18 at 19:35

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$\begingroup$"the biggest problems with anus speaking is that the colon is designed to be filled with solid waste and you'd basically be unable to speak without purging first" No, that would be just like a human speaking with their mouth full.$\endgroup$
– RenanDec 7 '18 at 20:13